CLASSIFICATION OF THE BACTERIA. 91 



g. Beggiatoa, Trev. 



Filaments very slender, surrounded by mucous mat- 

 ter, rigid, having oscillatory movements. Protoplasm 

 white, enclosing numerous granules, which recent 

 observations have demonstrated to be crystalline sul- 

 phur (Cramer, Cohn). 



The Beggiatoa are found most abundantly in 

 thermal sulphur waters,. where they constitute 

 flocculi, which have been named Glairine, Bare- 

 gine. They often live in water not containing 

 free oxygen. 



They play a great role in the elimination of 

 sulphur and the disengagement of sulphuretted 

 hydrogen in thermal waters. 



Their principal species are : — 

 B. alba, Trev. 



A whitish mucous mass enclosing colorless filaments, 

 having a diameter of 3.5 to 4 fi. In most thermal and 

 stagnant waters. 



B. arachnoidea, Rabh. 



Flocculi very minute, snow white, filaments as long 



as broad, — 5.4 to 7 //,. In the thermal waters of 



Europe. 

 B. nivea, Rabh. ; B. leptomitiformis, Trev., nearly related 



species, living in the same conditions. 



Cohn and Warming have also described : — 



B. mirabilis, Cohn, articles scarcely flexible, measuring 20 



to 40 p. 



B. minima, Warming, a very small species, very flexible ; 



length 40 /*, thickness 1.8 to 2 p. 



4. Spirobacteria. 

 This tribe includes the bacteria with undulating 

 filaments, or filaments in spirals, more or less de- 



